If the OP is interested in an Android device that has page turn buttons and that can be rooted, I can add two options: the Boyue T63 and the Onyx Boox C67ML Carta 2. Both have 6 inch displays with 300 dpi. Both have microSD card slots. Both run Android - though an "old" version (4.2.2). Both can be rooted. There's plenty of info in various MobileRead forums as to how to do that with each. Both work great with Calibre Companion.
Battery life? Not quite as good as what you might get from a Kindle or Kobo, but not bad. The Boyue has better battery life than the Onyx. As with most devices, turning off WiFi when not needed extends battery life.
The Onyx comes with Google Play Store pre-installed; the Boyue does not.
A lot depends on what matters most to the OP. If battery life outweighs having Android, then the Kobo might be a better pick. If the opportunity to install a few apps, like Moon Reader or Instapaper, appeals to the OP, then go with the Onyx or Boyue (though I understand that Kobos have Pocket integration).
Onyx makes e-readers of various sizes. A larger one might be better for any vision problems, but it will be more expensive. I don't have any serious vision problems, but I'm starting to wonder about getting something larger, like the H2O or Aura One. If vision problems are an issue, then I'd suggest a device larger than six inches. Again, it depends on one's priorities.
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